Glaucoma Eye Problems In Your Dog And Cat
Ron Hines DVM PhD
When the pressure of the fluid in the front chamber of your dog or cat’s eye rises – it is developing glaucoma. Any condition that interferes with the normal circulation of fluid in your pet’s eye can result in glaucoma. Glaucoma is a less common complaint in cats than in dogs; but veterinarians do not know if that is just because cat owners are less likely to notice the subtle early warning signs. (read here & here)
Glaucoma is a progressive disease that will, in most cases, eventually destroy your pet’s vision. Veterinarians in general practice can delay this as best they can with medication. But if you want to make every effort to preserve your pet’s vision as long as possible, have your regular veterinarian refer you on to a board-certified veterinary ophthalmologist as soon as glaucoma is suspected. But I want you to keep in mind that even if glaucoma does take your pet’s vision, your dog or cat with limited or no vision will remain just as happy and content.
What Are The Signs Of A Glaucoma?
The first sign that a pet is developing glaucoma is often an enlarged pupil that doesn’t constrict normally in bright light. The blood vessels on the affected eye are also often very inflamed or bloodshot.
Often, the problem is mistaken for conjunctivitis or an eye allergy. When these pets are given common steroid-containing eye drops, their eyes do look better – temporarily. Veterinarians see so many eye irritations that steroid-containing eye drops are frequently dispensed. However, it is wise to have the intraoccular pressure of your pet’s eye checked (with a tonometer) whenever there is even a slight suspicion that the problem might be more than simple conjunctivitis. This intraoccular pressure test is the only way glaucoma can be diagnosed early. By the time the eye actually enlarges, vision has been permanently lost.
If a developing glaucoma is not treated immediately, the pet’s eye will begin to look cloudy. By this time, vision is usually lost and can not be restored. This can all occur extremely fast – sometimes in less than one day. Ophthalmologists have a “30-30 rule”. If the pressure in your pet’s eye stays above 30 mm for thirty hours the pet is likely to loose vision in that eye.
What Are The Different Types Of Glaucoma That Develop In Dogs And Cats?
Glaucomas are divided as to being primary or secondary and as to being open angle or closed ( narrow) angle.
Primary glaucoma is an inherited problem. It is due to abnormal anatomy of the eye. We see it most often in cocker spaniels, basset hounds, Australian shepherds, chows, shar peis, Labradors and Nordic breeds. But any breed or cross bred can be affected. Glaucoma of this type usually begins in one eye – but eventually both eyes are involved and the result is complete loss of the pet’s vision. It is usually no more than 8 months until the second eye is involved. It is much less frequent in cats. Pets with this problem should not be bred.
Secondary glaucoma occurs when something occurs in the eye that prevents normal fluid flow and drainage. This can be a cataract, inflammation (uveitis) or trauma to the eye. In cats, uveitis is the most common cause. Uveitis in cats is often due to FIP .
Glaucoma is also divided into open angle and closed or narrow angle glaucoma. Narrow angle glaucoma is the most common in dogs although beagles have a high incidence of the open form.
How Is Glaucoma Diagnosed?
There is only one way to diagnose a glaucoma early enough so that there might be something that might help. It is by using a small devices called a tonometers that measures pressure within your pet’s eye.
This can be done in your veterinarian’s office. There are two types of tonometers. The older and still popular Schiotz type tonometer (which runs about $503), rests on your pet’s anesthetized cornea and measures the amount of indentation that a given test weight will cause in the pet’s cornea. The more the pressure within the eye, the less the cornea will indent. The much newer type that blasts a puff of air against the cornea similar to what your ophthalmologist uses is a device that not all veterinarians have access to (it costs upwards of $4,000). Both devices are equally accurate. (read here)
Checking eye pressure in your pet is not painful.The whole test only takes a minute or two. Once a drop of local anesthetic has been placed in your dog or cat’s eye, its head must be held steady to prevent eye injury. So a few dogs and cats might require tranquilization. However all calming medications can affect intraoccular pressure. So they are best avoided whenever possible. (read here and here)
Normal pressure (IOP, intra-ocular pressure) varies depending on the technique, but generally, a reading greater than 25 mm (25 mmHg) indicates glaucoma is present. Sustained pressure of 50 mm or greater permanently damages the optic nerve and retina. So with a reading of 50 or more, your dog or cat’s vision has already been permanently lost – or soon will be. If the test indicates that glaucoma is present, a second test, called gonioscopy will determine if the glaucoma is the wide angle or narrow angle type.
What Happens As Glaucoma Develops?
When your dog or cat develops the most common, narrow angle type glaucoma, pressure within its eye often rises quite suddenly. Dogs and cats that develop the much rarer form, open angle glaucoma, develop it slowly over a matter of months. The increased pressure that develops in both forms destroys the pet’s retina and optic nerve. Both forms are quite painful. Your pet might paw at its affected eye or rub its head along the floor. The blood vessels of the white portion of the eye (the sclera) often stand out prominently and the normally-clear window portion (the cornea) might become cloudy or bluish. Bright light might bother your pet. Some dogs and cats loose their appetite and become depressed due to the pain, but most are quite stoic. As this eye problem progresses, the affected eye will appear larger and the pupil will not contract (constrict) as it should in bright light. By the time this occurs, it is always too late to save the pet’s vision. This makes glaucoma a medical emergency. If the pressure in the eye has risen significantly, vision can be permanently lost within less than a day.
What Medications Are Available That Might Help My Pet?
Unfortunately, medical treatment of glaucoma works much better in people than it does in our dogs and cats. You probably know of a friend or relative with glaucoma whose vision has been preserved for many years with topical and oral medications. But dogs and cats usually have a different type of glaucoma than we do. And their type, narrow angle glaucoma, does not respond nearly as well to medications. In many cases, surgery to relieve the pressure is the only option that might benefit your pet.
Your Pet’s Treatment Plan depends on the stage of the problem. The Goals Of Treatment Are:
Reduce the pressure within your pet’s eye
Reduce the amount of aqueous fluid that your pet’s eye produces
Increase the amount of aqueous fluid drainage
Provide sufficient pain relief for your pet
Medications That Suppress Fluid Production Within The Anterior Portion Of The Eye:
These are also called aqueous formation suppressors and carbonic anhydrase inhibitors. They include Acetazolamide (Diamox®), Dichlorphenamide (Daranide®), dorzolamide HCl (Trusopt®), and brinzolamide (Azopt®). Timolol, a beta-adrenergic receptor blocker is commonly used for this purpose. Some (eg Timolol-dorzolamide) are used in combination with one or more of the other medications.
Medications That Constrict The Pet’s Pupil To Allow Better Anterior Eye Fluid Drainage:
These are also called miotics. They relieve pain and allow fluid in the eye to drain more freely. Pilocarpine is the miotic most often used in the treatment of canine glaucoma. Physostigmine and demacarium bromide are others.
Other Medications that decrease fluid Pressure In The Eye:
These are also called uveosclaeral outflow enhancers. Two are brimonidine tartrate (Alphagan®) and latanoprost
These medications are used in glaucoma emergencies to attempt to lower intraocular pressure rapidly. Mannitol, glycerol and urea are the ones most often used.
These medications are given to try to protect the vision-producing cells within the eye from death when pressure within the eye rises. This is still an experimental therapy. The medications are generally giving to promote blood supply to these cells. Some of these drugs are in a class called calcium channel blockers.
Because current medications have been so disappointing in halting glaucoma in dogs and cats, a number of surgical techniques are commonly attempted. These techniques try to destroy the cells in the front section of the eye (anterior chamber) that are producing the fluid (the ciliary bodies) and to open channels for excess fluid to leave the eye.
There are many variations of this surgery with various complicated names. If you go that route, once you have located a veterinary ophthalmologist in your area, that person will tell you which of these procedures she/he is most confident in using. The skill and experience of ophthalmic surgeons in performing the procedure is more important than the type of procedure they use. New techniques and materials are always being explored. The lack of reports of successful glaucoma surgery in dogs and cats demonstrates that none of these procedures have been very successful in preserving vision. At best, the affected visionless eye might not have to eventually be removed. (read here) I have cared for many dogs that have lost one or both eyes. Most of those were the short-snouted breeds like pekingese, lhasa apsos and shih tzus. With eyes lost, they continue to lead perfectly happy lives. When no vision remains in your pet’s eye(s), the goal of complex glaucoma surgery is to reduce pain and preserve cosmetic eye structure. Preserving the cosmetic structure of a blind eye in a dog or cat is performed to meet the psychological needs of the pet owner, not the pet. Less complex removal of the eye (enucleation) also renders your pet pain free.